In a phased array antenna system, the overall antenna system includes a plurality of different antenna elements that are individually steered to direct and/or receive a beam in a selected direction. By using a phased array antenna system, it is possible to reduce the side lobes and, thus, minimize any power that is wasted in the antenna system.
With this type of system, the antenna beam is steered by adjusting the relative phase shift of each antenna element through individual phase shifters that are connected to each antenna element. The arrays are also typically sensitive to frequency. To overcome any sensitivity to frequencies, the phased array antenna system typically will use time delay steering where the signals propagated in each antenna element are time delayed to create a time coherence, and thus, steer the antenna beam into the predetermined direction.
Some prior art phased array antenna systems use a switched line phase shifter having more phase at higher frequencies than at lower frequencies. These type of phased array antenna systems require more bits of phase shift to achieve the same amount of phase at low and high frequencies. This also creates a limit to the amount of beam forming that can be accomplished at any one frequency for a given bandwidth. Other prior art switched delay line phase shifters are designed for different subbands, but require complex, expensive and large switching networks or diplexers. Others are complex and heavy, some even using lumped elements, requiring broad band attenuators that are expensive and have a great signal loss, thus mandating increased gain requirements. Even others have used 0 to 180 degree hybrids, but only for narrow band applications.
One type of phased array antenna system uses time delay steering having a binary controlled and switched delay line. This system uses appropriately delayed signals in each antenna element channel and is disclosed in U.S. Pat. No. 3,295,138 to Nelson. Each switched delay line comprises a plurality of fixed time delays, which are combined to produce successive increments of delay in response to binary control signals.
It is also desirable to use a microstrip circuit to reduce the cost of implementing a phased array antenna system. Microstrip is less expensive than other known prior art construction techniques. An example of a microstrip phase shifter is disclosed in U.S. Pat. No. 3,568,105 to Felsenheid. In the '105 patent, a reflective system is used, but does not disclose a switched line phase shifter with any time delay. The '138 patent, on the other hand, does disclose a switched line phase shifter that switches between two line lengths. However, the structure disclosed in the '138 patent works primarily on one frequency and has a more exact differential phase, and is thus limited to a narrow band area. It would be advantageous if a switched delayed line phased array could be used with a wideband system in a low cost microstrip.
It is believed that some prior art phased array antenna systems provide some phase shifting using filters as a phase shift element, and provide phase performance in the 100 MHZ to 300 MHZ frequency range with reduced size, such as possibly found on microstrip. This type of phase shifter can be used as a phase shifter in either a switched or series digital configurations, and contains individual filters with controlled phase shift values. Typically, the phase shifters are placed in tandem, with progressively greater phase shift angles to provide phase angle selectivity. However, it is desirable to form a structure that can be used with a wide range of frequencies, such as broad band in one or two GHz, and positioned on a microstrip conductor.